The discovery of antibiotics has been one of the greatest achievements of modern medicine, but their excessive use has selected for resistant bacteria. Cases of infection due to multiply resistant organisms, such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE), continue to increase. At the same time, there has been a decline in the development of new antibacterial therapies.
Antimicrobial peptides (AMPs), in place of antibiotics, act as the first line of defense against invading pathogens, and also help to modulate host immune responses. One of the AMPs, Epinecidin (Epi)-1, is a 21-amino-acid peptide that was first identified in a fish species, grouper (Epinephelus coioides) [Pan et al., Gene expression and localization of the epinecidin-1 antimicrobial peptide in the grouper (Epinephelus coioides), and its role in protecting fish against pathogenic infection. DNA Cell Biol 2007, 26:403-13; or Taiwan Patent No. I-299335.] Structurally, the peptide is similar to pleurocidin, a protein of the winter flounder (Pleuronectes americanus). Synthetic Epi-1 exerted immunomodulatory and protective effects against infection with Gram negative bacteria in several hosts, including Pseudomonas aeruginosa infection in mice, Vibrio vulnificus infection in zebrafish, and Riemerella anatipestifer infection in duck [Lin et al., Epinecidin-1, an antimicrobial peptide from fish (Epinephelus coioides) which has an antitumor effect like lytic peptides in human fibrosarcoma cells. Peptides 2009, 30:283-90; Lee et al., The antimicrobial peptide, epinecidin-1, mediates secretion of cytokines in the immune response to bacterial infection in mice. Peptides 2012, 36:100-8; Pan et al., Insights into the antibacterial and immunomodulatory functions of the antimicrobial peptide, epinecidin-1, against Vibrio vulnificus infection in zebrafish. Fish Shellfish Immunol 2011, 31:1019-25; Pan et al., Antimicrobial peptides of an anti-lipopolysaccharide factor, epinecidin-1, and hepcidin reduce the lethality of Riemerella anatipestifer sepsis in ducks. Peptides 2010, 31:806-15]. It was also confirmed that oral administration of recombinant Epi-1 protected grouper (Epinephelus coioides) and zebrafish (Danio rerio) from Gram negative Vibrio vulnificus infection [Pan et al., Oral administration of recombinant epinecidin-1 protected grouper (Epinephelus coioides) and zebrafish (Danio rerio) from Vibrio vulnificus infection and enhanced immune-related gene expressions. Fish Shellfish Immunol 2012, 32:947-57.] Epi-1 also exhibited antibacterial activity against Gram positive strains, as well as antifungal and antiviral activity [Pan et al., In vitro activities of three synthetic peptides derived from epinecidin-1 and an anti-lipopolysaccharide factor against Propionibacterium acnes, Candida albicans, and Trichomonas vaginalis. Peptides 2009, 30:1058-68; Wang et al., Inactivation of nervous necrosis virus infecting grouper (Epinephelus coioides) by epinecidin-1 and hepcidin 1-5 antimicrobial peptides, and downregulation of Mx2 and Mx3 gene expressions. Fish Shellfish Immunol 2010, 28:113-20; Pan et al., Evaluation of the epinecidin-1 peptide as an active ingredient in cleaning solutions against pathogens. Peptides 2010; 31:1449-58]. Moreover, Epi-1 was reported to promote resistance to bacterial infections by stabilizing the cytoskeleton network in host cells [Huang and Chen, Proteomic and functional analysis of zebrafish after administration of antimicrobial peptide epinecidin-1. Fish Shellfish Immunol 2013, 34:593-8].
Pardaxin is also known as GE33, as it is a 33 amino acid peptide that starts with glycine (G) and ends with glutamic acid (E) [Oren and Shai, A class of highly potent antibacterial peptides derived from pardaxin, a pore-forming peptide isolated from Moses sole fish Pardachirus marmoratus. Eur J Biochem 1996, 237: 303-10, or U.S. Pat. No. 6,172,038]. GE33 is a pore forming peptide with an a-helix structure, which confers selective cytolytic activity against bacteria [Oren et al., A repertoire of novel antibacterial diastereomeric peptides with selective cytolytic activity. J Biol Chem 1997, 272: 14643-9]. GE33 was reported to have antimicrobial activity against both Gram-positive and -negative bacteria. Furthermore, clinical case studies have shown that application of GE33 to severely infected cutaneous wounds can clear the infection and improve healing. Thus, GE33 has many features consistent with antibiotics, but potentially has broader applications, and may avoid or reduce concerns of bacterial resistance [Hsu et al., Pardaxin-induced apoptosis enhances antitumor activity in HeLa cells. Peptides 2011, 32: 1110-6; Huang et al., Pardaxin, an antimicrobial peptide, triggers caspase-dependent and ROS-mediated apoptosis in HT-1080 cells. Mar Drugs 2011; 9: 1995-2009; Shai and Oren, Diastereoisomers of cytolysins, a novel class of potent antibacterial peptides. J Biol Chem 1996; 271: 7305-8].
Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of infection in injured patients, and healthcare associated (HA) and community associated (CA) MRSA have become prevalent in recent years. Its emergence is a consequence of excessive use of certain antibiotics. MRSA generally does not cause infection in the absence of injury. When MRSA enters the body through a cut or abrasion, it may cause infection by evading the natural protective mechanisms of the body. This necessitates the use of alternative therapies, which ideally do not result in resistance through continuous selective pressure. MRSA infections in recent years have been treated with mupirocin, clindamycin, trimethoprim/sulfamethoxazole, doxycycline, minocycline, linezolid, vancomycin, daptomycin, and telavancin [Bjorn et al., Anti-infectious and anti-inflammatory effects of peptide fragments sequentially derived from the antimicrobial peptide centrocin 1 isolated from the green sea urchin, Strongylocentrotus droebachiensis. AMB Express 2012, 2:67]. Also, vancomycin, linezolid, daptomycin (Cubicin), tigecycline (Tygacil), and telavancin (Vibativ) were reported to treat severe MRSA infections of skin and soft tissue in hospitals. Vancomycin, the primary treatment for MRSA, possesses high minimum inhibitory concentration (MIC) values and other limitations [Palazzolo-Ballance et al., Neutrophil microbicides induce a pathogen survival response in community-associated methicillin-resistant Staphylococcus aureus. J Immunol 2008, 180:500-9]. Induction of AMP (e.g., cathelicidin) release in response to cutaneous skin injury has been documented; however, the effect of AMPs on MRSA infection has been incompletely studied [Dorschner et al., Cutaneous injury induces the release of cathelicidin anti-microbial peptides active against group A Streptococcus. J Invest Dermatol 2001, 117:91-7.27]. Accordingly, there is no way to confirm which of AMPs is effective in wound healing, particularly in burns.